The present invention relates to heat transfer recording, and more particularly, to improved ink compositions for heat transfer recording and reusable heat transfer recording ink sheets containing such ink compositions.
As is well-known in the art, the heat transfer recording process is extensively used for various recording purposes. This recording process features both such principal advantages as easy and simple procedures and inexpensiveness as a result for intense of use of plain paper as recording material, and such additional advantages as good retention of the formed recording. Such a recording process can be effectively used in a wide range of image recording fields.
Even the heat transfer recording process, however, has shortcomings. For example, the process has conventionally made use of ink sheets wherein a single transfer recording step transfers all the ink composition from areas of the substrate of the ink sheet corresponding to the recorded pattern to the receiver sheet while ink composition still remains from areas of the substrate of the ink sheet not corresponding to the recorded pattern. The lack of its uniform, overall distribution makes it impossible to use the ink sheet in a succeeding transfer recording step. Therefore, ink sheets of this type must be disposed of after a single use. Such so-called single-use ink sheets are considered expensive to the users.
Recently, methods for the provision of reusable heat transfer recording ink sheets have been proposed. One well-known method provides for the repeated supply of additional ink composition to the ink sheet after each transfer recording step. However, the supply procedure is troublesome since a new ink composition must be continuously and uniformly coated on the substrate of the ink sheet after each transfer recording step. Further, complicated supply devices and related equipment are necessary. Therefore, while this method enables the repeated use of ink sheets, it detracts from the overall advantages of the heat transfer recording process itself.
A more advanced method, known from Japanese Patent Application Laid-Open Gazette No. 55-105579, provides for the ink to be contained in a plurality of pores formed within the polymeric film. The ink may be expressed under pressure. This process utilizes the ability of the pores to retain to enable reuse of ink sheets. However, the formation of a porous resin layer on polymeric film is complicated, and the uniform filling of the ink into the pores of the formed resin layer is difficult.